1. Field of Invention
This invention relates to optical transmission systems and, more particularly to bi-directional optical transmission systems.
2. Description of Prior Art
To reduce component count and material cost of optical communication systems, a bi-directional transceiver is often used, where incoming and outgoing beams share a single transmission path. Schairer, in U.S. Pat. No. 6,301 ,035 (2001), and Jokerst et al., in U.S. Pat. No. 6,721,503 (2004), disclosed such a transceiver, which stacks an emitter chip, e.g. a laser or LED chip, on a photo detector chip. Since it doesn't need a beam splitter to create separate optical paths for a light source and detector, the structure is compact and it reduces redundant parts. The scheme works well when an incoming beam has a large beam size and the detector chirp is bigger than the emitter chip, because the latter sits in front of the former.
In many systems however, an emitter chip heats itself up easily due to power consumption. So a thermoelectric (TE) cooler is often needed to control the chip temperature. A TE cooler, a heat conductive submount, and an emitter chip are usually bonded together to form an emitter subassembly, which, in most cases, is much larger than a detector chip. The bulky emitter subassembly makes it impossible to sit atop a detector chip and build a compact transmission system.
Therefore, there exists a need for a bi-directional transmission system which is able to have a relatively large emitter subassembly comprising an emitter, a submount, and a TE cooler.